Tissue removing catheter and RF cutting method

ABSTRACT

An atherectomy device includes a catheter with a window at its distal tip for admitting tissue into a catheter compartment. A cylindrical cartridge in the compartment has a cutting edge that supports an electrically conductive cutting element, e.g. a band or wire. The cutting element and adjacent tissue can be heated to a selected temperature by generating an electrical current through the cutting element. The catheter is maneuverable to position its distal end near a lesion in an artery. The catheter incorporates a dilatation balloon or other feature to urge the catheter against the lesion, so that at least part of the lesion enters the compartment through the window. Then, the cartridge is manipulated from the catheter&#39;s proximal end to move the cutting edge across the window, severing the acquired tissue. According to alternative embodiments, the cartridge is either rotated or moved axially relative to the catheter, in either event closing the catheter window when the cut is complete. Further alternatives involve either placing an indifferent electrode on the patient and providing an RF signal via a single conductor to the cutting element for ohmic heating, or providing an RF (or a DC) current through the cutting element and two separate conductors for direct resistive heating of the cutting element.

This is a Divisional of application Ser. No. 08/376,226, filed Jan. 23,1995 and now U.S. Pat. No. 5,665,062.

BACKGROUND OF THE INVENTION

The present invention relates to devices for removing obstructions frombody lumens, and more particularly to catheters for removingatherosclerotic plaque and thrombotic occlusions from blood vessels.

Atherectomy catheters are known for their utility in removingatherosclerotic plaque and thrombotic occlusions from arteries. Whileintended mainly for use in the coronary arteries, such catheters may aswell be used in peripheral vessels. Beyond coronary uses, such catheterscan have neurological applications, e.g. removal of lesions in carotidarteries, gynecological use in recanalizing fallopian tubes, and apotential urological application for removal of benign prostatehyperplasia.

Atherectomy catheters have a variety of designs. According to onedesign, the catheter has a rounded or bullet shaped tip with an abrasivesurface. At the treatment site, the tip is rotated at high speed andburrows through the occlusion. The resulting debris, typically inparticulate form, is not captured by the device. Rather, it is allowedto flow to the capillary bed where it is absorbed. The device is mosteffective in abrading hardened (calcified) occlusions, with the intentbeing to produce particulate debris no larger than about 7 microns indiameter. When encountering softer occlusions, however, the devicepresents the risk of an occlusion breaking off during the atherectomyprocedure, causing an acute and potentially life-threatening reclosureof the artery. The abrasive tip may inadvertently remove endotheliumcells during catheter insertion, use or removal, thereby creating sitesfor potential lesions.

A second type of catheter employs a cartridge housed within thecatheter, near the catheter distal tip. When the distal tip region isplaced near the occlusion, plaque enters the cartridge through anopening or "cutting window". A cup-shaped blade then is rotated oroscillated at high speed, and advanced to cut and capture plaque thatentered the cartridge. U.S. Pat. No. 5,312,425 (Evans); U.S. Pat. No.5,087,265 (Summers); and U.S. Pat. No. 5,085,662 (Willard) discloseversions of atherectomy catheters with a movable blade or cartridgewithin a tissue collection volume near the catheter distal tip.

An example of an atherectomy catheter that depends on vaporization ofplaque is found in U.S. Pat. No. 5,087,256 (Taylor). A dome-shaped headon the tip can be heated to temperatures in the range of 300-400 degreesC., for disintegrating plaque. U.S. Pat. No. 5,098,431 (Rydell)discloses a catheter in which an RF discharge between two spaced apartannular electrodes, electrosurgically cuts tissue to remove a blockage.

Conventional atherectomy catheters are limited principally to an axialcutting direction and subject to smooth cell muscle migration(restonosis) after treatment. Patients treated with conventionalatherectomy devices have restonosis rates of 30-40 percent within thesix months following treatment.

Therefore, it is an object of the present invention to provide anatherectomy catheter with a cutting edge that achieves a finer, moreaccurate cutting of unwanted tissue, to reduce the risk of acuteblockage due to the breaking off of an occlusion.

Another object is to provide a tissue cutting element for an atherectomycatheter that is effective in severing calcified and soft occlusions.

A further object is to provide a flexible atherectomy catheter thatincorporates means for capturing tissue being severed, to ensure againstthe escape of such tissue into the blood stream.

Yet another object is to provide an atherectomy catheter with enhancedversatility, due to the incorporation of longitudinal and transverse(arcuate) tissue cutting motions.

Further, it is an object of the present invention to provide anatherectomy catheter and procedure tending to seal the region of thecut, thus tending to reduce the incidence of restonosis.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a device forremoving atheromas from a body lumen. The device includes an elongatecatheter having a proximal end and a distal end. The catheter has a wallthat defines a compartment within the catheter near its distal end, anda window is formed through the catheter wall to allow entry into thecompartment. The catheter incorporates an electrically conductive tissuecutting element. A means is provided for generating an electricalcurrent in the cutting element to heat the cutting element and adjacenttissue at least to a selected temperature above normal body temperature(i.e. 37 degrees C.). A carrier is mounted movably relative to thecatheter, for supporting the cutting element proximate the window andfor a controlled movement of the cutting element along and adjacent thewindow. The catheter is flexible and maneuverable to locate its distaltip within a body lumen and to place the window against a tissue wallsegment of the body lumen to acquire tissue within the compartment. Thecutting element, when heated and when undergoing the controlledmovement, severs the acquired tissue.

There are several suitable approaches for generating the currentnecessary for cutting. At present, the most preferred approach involvesa biocompatible cutting element (e.g. of platinum) subjected to RFenergy in combination with an indifferent plate electrode on thepatient's back. Application of the RF energy causes ohmic heating oftissue near the cutting element as current passes through the tissue.

As an alternative, RF energy can be applied to heat an electricallyresistive cutting element formed of nickel or a nickel chromium alloy.In this approach, the cutting element is heated to a temperaturesufficient to sever a lesion that comes into contact with the element.As a third and presently least preferred alternative, DC power isapplied to heat an electrically resistive cutting element, again ofnickel or a nickel chromium alloy. For biocompatability, an insulativejacket or coating is applied to the nickel or nickel chromium cuttingelement.

The preferred cutting element is a flat band, having a thickness ofabout 0.015 inches and a substantially greater width. The band achievesa highly accurate and fine cut of the tissue, considerably reducing thepulling and tearing of tissue as compared to the conventionaloscillating or rotating blades. Unwanted tissue is severed more cleanly,reducing patient risk. Further, it is believed that the elevatedtemperatures of the band and adjacent tissue have a sealing orcauterizing effect along the region of the cut. This is believed toresult in a substantial reduction in restonosis in the treated artery.

As an alternative to a flat band, the cutting element can be a fine wirehaving a diameter of about 0.030 inches or less to provide the cuttingedge.

The carrier preferably includes a cartridge contained within thecompartment. The cartridge can have an axially extended cartridge wall,a cartridge opening and a cutting edge along the cartridge opening forsupporting the cutting element. A control means is coupled to thecartridge proximal end, and operable to selectively position and movethe cartridge within the compartment, to provide the controlled movementof the cutting element. Preferably the cartridge wall is longer axiallythan the window, so that the cartridge can be positioned tosubstantially close the window and thus capture severed tissue. Withtissue secured in this manner, there is no need for a suction device orother means to withdraw tissue proximally through the catheterimmediately after it is cut. With no need to pay attention to a vacuumor suction means, the physician is able to direct more attention to theatherectomy procedure at hand.

Conversely, a vacuum means (or alternatively a plunger device and adiaphragm valve) may be provided if desired for removing severed tissuefrom the compartment, to allow cutting and removal of tissue at severallocations during a single procedure.

There are several alternatives for supporting the cutting element. Forexample, the cutting edge can be the leading or distal edge of thecartridge, preferably but not necessarily annular. In this event, thecartridge is moved distally to provide the necessary controlled movementof the cutting element. Alternatively, the cutting edge can be an axialedge of the cartridge opening, in which event the cartridge is rotatedabout a longitudinal axis to move the cutting element in an arcuatepath.

A preferred control means includes an elongate drive member, e.g. a rod,coil or tube, attached to the proximal end of the cartridge andextending proximally to a proximal end of the catheter. The member canbe rotated, pushed or pulled at the catheter proximal end, to impartlike motion to the cartridge.

Another aspect of the invention is a process for removing tissue from abody lumen, according to the following steps:

a. providing, near a distal end of an elongate catheter, a compartmentand a window to the compartment through a catheter wall, and anelectrically conductive tissue cutting element mounted to the catheterfor a controlled movement of the cutting element adjacent and along thewindow;

b. inserting the catheter into a body lumen, and guiding the catheter toposition the window against a tissue wall segment of the body lumen,thus to cause tissue to enter the compartment via the window and occupythe compartment;

c. generating an electrical current in the cutting element to heat thecutting element and adjacent tissue at least to a selected temperatureabove normal body temperature, while causing the cutting element toundergo the controlled movement, thereby to sever the tissue occupyingthe compartment.

After the tissue is severed, the compartment can be closed to preventegress of the severed tissue. The controlled movement of the cuttingelement can be one of two alternatives: substantially linear and axialwith respect to the catheter, or arcuate about an axis runninglongitudinally of the catheter.

Thus in accordance with the present invention, there is provided anatherectomy device and procedure suitable for treating soft occlusionsand calcified occlusions alike, with clean and accurate cutting thatreduces the risk of tissue tearing and escaping into the blood vesselunder treatment. The catheter is versatile, due to its flexibility fortraversing tortuous vessels and for the ability to cut in either anarcuate or axial path. The application of heat is concentrated along theregion of the cut, i.e. the cutting element and adjacent tissue,reducing the required cutting force, increasing cutting accuracy andtending to cauterize or seal the region of the cut, thus tending tosubstantially prevent restonosis.

IN THE DRAWINGS

For a further understanding of the above features and advantages,reference is made to the following detailed description and to thedrawings, in which:

FIG. 1 is an elevation of an atherectomy device constructed inaccordance with the present invention;

FIG. 2 is a sectional view taken along the line 2--2 in FIG. 1;

FIGS. 3 and 4 are sectional views taken along the lines 3--3 in FIG. 1and 4--4 in FIG. 2;

FIG. 5 is a perspective view of a tissue retaining cartridge employed inthe device;

FIG. 6 is a schematic view illustrating circuitry for providing anelectrical current through a mounted heating element on the cartridge;

FIGS. 7-9 are diagrammatic views illustrating use of the device;

FIG. 10 is an elevational view of the distal end region of analternative atherectomy device constructed according to the invention;

FIG. 11 is a sectional view taken along the line 11--11 in FIG. 10;

FIG. 12 is a perspective view of a tissue retaining cartridge used inthe device of FIG. 10;

FIGS. 13 and 14 diagrammatically illustrate use of the device of FIG. 9;

FIG. 15 is a three-dimensional illustration of an alternative embodimentcartridge; and

FIG. 16 is a schematic view of an alternative circuit for heating thecutting element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, there is shown in FIG. 1 an atherectomydevice 16 for removing unwanted tissue from body lumens, moreparticularly blood vessels. The device includes a control housing orhandle 18, and an elongate and pliable catheter 20 connected at itsproximal end to the handle.

Catheter 20 is formed of a biocompatible polymer such as Pebax (brandname) polyether block amides, Pellethane (brand name) polyurethane orpolyimide, and can have an outside diameter in the range of 3 Fr. (1 mm)to 8 Fr. (2.7 mm) or larger. Catheter 20 includes several lumens thatrun axially from handle 18 to a distal end region 22. A guidewire 24,contained within one of the lumens, extends proximally beyond handle 18and distally beyond a tapered distal tip 26 of the catheter. Furtherlumens are provided in the catheter, for delivery of contrast fluid ortreatment fluid to the distal end region, and for balloon inflation.While not shown, a braided or other filament structure can be embeddedinto the catheter body to enhance torque transmission, if desired.

A window 28 is formed through a wall 30 of the catheter along the distalend region. Window 28 is elongate in the axial direction and extendsalong about forty percent of the circumference of catheter wall 30. Acartridge or cutting sleeve 32 is contained within catheter 20. Thecartridge is shown adjacent and along window 28, but is movable axiallyrelative to the catheter. This enables a proximal retraction of thecatheter from window 28, to open the window whereby the catheter canacquire tissue. An elongate drive rod 34, contained within a lumen ofcatheter 20, is coupled to the proximal end of cartridge 32 and extendsproximally through the catheter and into handle 18.

Drive rod 34 is formed of an electrically insulative material, e.g. aPTFE coated wire coil or spiral wrapped polyimide. The drive rod has ahigh degree of bending elasticity to permit its movement (with theremainder of catheter 20) along serpentine passages toward an intendedtreatment site. At the same time, drive rod 34 is sufficiently rigid inthe axial direction to permit controlling the cartridge axial positionby manipulating the drive rod at its proximal end. Drive rod 34 isconstructed of an electrically insulated material. A pair of conductors36 and 38, preferably polyimide jacketed copper or copper-clad steelwires, are bonded to the drive rod and electrically isolated from oneanother. Conductors 36 and 38 extend along the entire catheter length tocontrol housing 18.

A dilatation balloon 40 is formed to extend axially along distal endregion 22, axially aligned with window 28 but also spaced apartangularly 180 degrees, i.e. on the opposite side of the catheter fromthe window. Balloon 40 is inflated using a fluid supplied to the balloonunder pressure via a lumen of catheter 20.

A fluid port 42 admits contrast or treatment fluids in the region justproximally of window 28, while such fluids can be administered distallyof the window via the guidewire lumen.

Control housing 18 includes three branches for coupling two sources offluid (not shown): a branch 44 for balloon inflation, and two branches46 and 48 for delivery of contrast fluids or treatment fluids such asheparin. At the proximal end of the control housing is a connector 50with two electrically independent paths coupled to conductors 36 and 38,respectively. A line 52 (e.g. coaxial) removably electrically couplesconnector 50 to a power supply 54. Power supply 54 preferably is an RFsource, but can be a DC source as well. Also mounted at the housingproximal end are a fitting 56 and a control knob 58. Knob 58, coupled tothe proximal end of drive rod 34, is movable axially relative to fitting56, to control the axial position of cartridge 32.

A display 60 (e.g. LED) indicates the temperature of a cutting elementmounted to the cartridge. A temperature control 62 adjusts the currentthrough the cutting element, thus to set the cutting elementtemperature.

FIG. 2 shows several lumens running through the catheter, including aguidewire lumen 64 that also can be used to administer contrast andtreatment fluids. A control lumen 66 accommodates drive rod 34. Furtherlumens include a balloon inflation lumen 68 and an upper infusion lumen70 for providing fluids to fluid port 42.

As seen in FIGS. 3 and 4, control lumen 66 along the distal end regionforms a compartment 72 to accommodate cartridge 32. The compartmentextends distally beyond window 28 a slight distance, and extendsproximally of the window a sufficient amount to allow cartridgeretraction, i.e. placing the complete cartridge proximally of thewindow.

Cartridge 32 is cylindrical, having an axial wall 74 and a disk-shapedproximal wall 76. As seen in FIG. 5, cartridge 32 is open at its distalend to provide a circular cutting edge 78. A tissue cutting element,more particularly a fine, flat band 80, is mounted to the cutting edgeto form an arc. Band 80 need not circumscribe the cutting edge, butshould extend a sufficient amount to span window 28. Band 80 has athickness of about 0.015 inches, and is formed of nickel or a nickelchromium alloy coated for biocompatability. Alternatively (in anindifferent electrode approach discussed below) the band can be formedof platinum or another electrically conductive and body compatiblematerial. The band is heated when subject to an electrical current. Asan alternative to the band, the cutting element can be a wire with adiameter of at most 0.030 inches.

The polymer forming cartridge 32 can be blended with barium sulphate,bismuth trioxide or another suitable radiopaque material to facilitatefluoroscopic observation of the cartridge position before and duringtissue removal. Radiopaque markers also may be placed along thecartridge cutting edge and on corresponding (distal and proximal, orintermediate) edges of the window. Along with aiding accuratepositioning, these markers are useful in confirming when the cartridgeis closed after cutting.

Conductors 36 and 38 are coupled to opposite ends of cutting element 80.As indicated in broken lines, conductors 36 and 38 are embedded in axialwall 74 which, like the drive rod, is electrically insulative. Athermocouple 82 can be mounted to the cartridge near cutting edge 78 andpreferably bonded to cutting element 80, to monitor the cutting elementtemperature. Conductors 84, embedded in the cartridge and the drive rod,permit the cutting element temperature to be monitored from controlhousing 18. Alternatively, thermistors can be used to sense temperature.Further, for a resistive cutting element (i.e. nickel or nickelchromium) a characteristic dependence of resistance upon temperature canbe used to monitor the cutting element temperature.

Tissue is cut by advancing cartridge 32 distally from the retractedposition, with cutting element 80 and adjacent tissue maintained at atleast a predetermined temperature above body temperature. A circuit forheating the cutting element and tissue is schematically illustrated inFIG. 6. A controller 86 adjusts power from supply 54 as required, forgenerating current through cutting element 80 in an amount selected toheat the cutting element to the predetermined temperature. Thermocouple82 senses the temperature and provides the corresponding temperaturereading at display 60. If the display indicates a need to increase orreduce the temperature, controller 86 is adjusted to alter the currentaccordingly. A broken line at 88 indicates that if desired, the outputof thermocouple 82 can be employed to automatically adjust the cuttingelement current.

The use of device 16 to remove unwanted tissue is shown in FIGS. 7-9,where catheter 20 has been either steered or moved over guidewire 24 toa treatment position near a lesion 90 in a coronary artery. Catheter 20is manipulated from housing 18 to axially and angularly align thecatheter and lesion 90, so that window 28 faces the lesion (FIG. 7). Atthis point, dilatation fluid is supplied to expand balloon 40 against anarterial wall 92 opposite the lesion (e.g. as in aforementioned U.S.Pat. No. 5,085,662). Balloon dilatation drives the catheter distal endupward as viewed in FIGS. 7-9, forcing the catheter against the arterialwall about lesion 90 and causing at least a portion of the lesion toenter compartment 72 through window 28.

With tissue thus acquired, cartridge 32 is advanced distally from theretracted position, while cutting element 80 is maintained at theselected temperature, from 50-600 degrees C. and more preferably 50-400degrees C. This heating of the wire and adjacent tissue considerablyenhances the cutting of tissue. Moreover, the heating has a cauterizingeffect at the region of the cut and thus tends to seal the wound almostimmediately after cutting, to significantly reduce smooth cell musclemigration or restonosis after treatment. The minute filament results ina precise, well defined cutting path that minimizes stretching andtearing of tissue. Accordingly, cutting element is effective in severingsoft tissue as well as calcified or hardened tissue. This minimizes therisk of tissue fragmenting into particles or pieces that escape into thebloodstream.

Cartridge 32 is advanced until cutting edge 78 is distally of window 28(FIG. 9), to completely acquire severed tissue within the cartridge.During or following the cut, a treatment fluid may be administeredthrough lumens 64 and 70. After balloon deflation, the cartridge can beproximally withdrawn to remove the severed tissue.

In addition to the cauterizing/sealing effect, a salient feature of theinvention is the continuity of axial wall 74, which closes window 28when the cartridge is completely advanced. This insures that severedtissue remains captured within compartment 72 as the catheter iswithdrawn, thus to eliminate the risk that severed tissue will enter thebloodstream.

FIG. 10 illustrates, in axial (longitudinal) section, the distal endregion of an alternative device 96. This device differs from device 16in several respects concerning primarily the catheter distal end, butalso as to the manner of controlling the cartridge. A catheter 98 ofdevice 96 has flexible band 100 along its distal end in lieu of adilatation balloon. Band 100 can be flexed radially away from thecatheter and, upon contacting an artery, drives the catheter toward theopposite end of the artery. An example of such band and its control isfound in U.S. Pat. No. 5,087,265 (Summers).

A single, central lumen 102 accommodates the guidewire and is enlargedto provide a compartment 104. The compartment accommodates a cartridge106 having an axially extended wall 108, a proximal end wall 110 and adistal end wall 112. A drive tube 114, connected to the proximal endwall, is manipulated at the housing to selectively position cartridge106.

Drive tube 114 is used to rotate cartridge 106 about a longitudinalaxis, rather than to move the cartridge axially. Consequently, while itrequires less axial stiffness than drive rod 34, drive tube 114 must beresistant to torsional bending to apply the necessary torque to rotatecartridge 106. Also because of the lack of axial movement, compartment104 need not extend proximally beyond window 116 to accommodate thecartridge length. As seen in FIGS. 11 and 12, cartridge wall 108 is openalong a portion of its circumference, to provide an arcuate cartridgeopening 118 defined by end walls 110 and 112 and axial edges 120 and122. Axial edge 120 provides the cutting edge, and supports a linearcutting element 124. Cutting element 124 is flat and thin (e.g. 0.015inches thick), with a rectangular profile, to provide a lower profilecutting edge as compared to a wire.

FIGS. 13 and 14 illustrate the use of catheter 98 to remove a lesion 126from an artery 128. The catheter is positioned to axially align window116 with lesion 126, and further to angularly align the window andlesion. A control knob (not shown but similar to knob 58) is turnedrather than pushed or pulled, to angularly align cartridge 106 such thatopening 118 coincides with window 116 (FIG. 13). At this point, band 100is flexed to urge the catheter upwardly against the arterial wallwhereby a portion of lesion 126 enters compartment 104.

At this point, the knob is turned to rotate cartridge 106 clockwise asviewed in FIG. 13 while cutting element 124 is heated, thus toprogressively cut the lesion. Cartridge rotation continues until cuttingedge 120 is carried beyond the clockwise edge of window 116, whichcloses the window and captures acquired tissue. Then, catheter 98 isproximally withdrawn to remove captured tissue, or a plunger is used toremove tissue from the cartridge.

FIG. 15 illustrates an alternative embodiment cartridge 130 having anaxial wall that is open at the distal end and along part of itscircumference to define two cutting edges 132 and 134. A continuous wire136 (0.030 inch diameter) is mounted to the cartridge and shaped toprovide an arcuate segment 138 mounted to cutting edge 132, and a linearsegment 140 along axial cutting edge 134. Accordingly, cartridge 130 canbe used to effect axial cutting and arcuate cutting. Cartridge wall 142is continuous over at least sixty percent of its circumference to enableaxial and angular positioning that closes the associated catheterwindow, to insure capture of severed tissue. Drive member 144 can be atube, rod or coil and has sufficient axial and torsional rigidity toimpart axial and rotational movement to the cartridge.

FIG. 16 illustrates an alternative circuit for heating an arcuatecutting element 146. A conductor 148 connects the cutting element withan RF power supply 150. A second conductor 152 couples the power supplyand an indifferent electrode 154. The indifferent electrode preferablyis an electrode plate, typically applied to the back of the patient. Thepower supply provides an RF signal to the cutting element via conductor148. The signal returns to the power supply via conductor 152. Betweencutting element 146 and indifferent electrode 154, current flows throughbody tissue. Consequently, ohmic heating of tissue is the primary factorin raising the temperature of tissue adjacent the cutting element to thepredetermined or desired level. Cutting element 146 preferably isplatinum, for high biocompatability and electrical conductivity.Accordingly cutting element heating from the current, while present to adegree, is slight compared to the ohmic heating effect. A controller 156governs power supply 150 to provide the appropriate current in cuttingelement 146. While not shown in FIG. 16, a thermocouple or other sensingelement can be mounted at the cutting element, to sense the temperatureof the cutting element and adjacent tissue, and provide feedback tocontroller 156. As noted above, this approach (highly conductive cuttingelement and indifferent electrode) is presently the most preferred.

While the disclosure has focused on the treatment of coronary arteries,it is to be appreciated that devices in accordance with the presentinvention can be used to treat peripheral arteries and other vessels.These principles further can be applied in constructing and utilizingdevices in neurology for removal of lesions in the carotid arteries, ingynecology for recanalization of Fallopian tubes, and in urology forremoval of benign prostrate hyperplasia. The heating of the cuttingelement and adjacent tissue provides a fine, accurate cut to severtissue at minimal risk of forming fragments, and provides a sealingaction believed to reduce the incidence of restonosis. The cartridge canbe either rotated or moved axially of the catheter, for greaterversatility in severing unwanted tissue. After the cut, the cartridgecompletely closes the tissue-admitting window of the catheter, to insurecomplete capture of severed tissue.

What is claimed is:
 1. A device for removing unwanted tissue, including:an elongate catheter having a proximal end and a distal end, a catheter wall defining a compartment within the catheter, and a window through the catheter wall to allow entry into the compartment; a cartridge within the compartment, said cartridge having a cartridge wall, a cartridge opening for receiving tissue, and a cutting edge along the cartridge opening; a control means coupled to the cartridge and operable to selectively position and move the cartridge, for providing a controlled movement of the cutting edge along an adjacent window; and a tissue heating means comprising a cutting element disposed along the cutting edge and an energy source operatively coupled to the cutting element to heat the cutting element and thereby heat tissue adjacent the cutting edge at least to a selected temperature above normal body temperature, and to maintain said tissue adjacent the cutting edge at least at the selected temperature during said controlled movement.
 2. The device of claim 1 wherein:the catheter is maneuverable to locate the distal end of the catheter within a body lumen and to place the window against a tissue wall segment to acquire tissue within the compartment, and the cutting edge, when undergoing the controlled movement, severs the acquired tissue; and said control means is operable to move the cartridge between an open position for permitting entry into the compartment via the window, and a closed position in which the cartridge wall closes the window.
 3. The device of claim 1 wherein:the cutting edge is part of the cartridge wall and leads the cartridge wall when undergoing the controlled movement.
 4. The device of claim 3 wherein:the cutting edge is a distal edge of the cartridge, and the controlled movement of the cutting edge is in the distal direction.
 5. The device of claim 3 wherein:the cartridge is cylindrical and substantially coaxial with the catheter, the catheter wall extends axially and is open along a portion of its circumference to form the catheter opening, the cutting edge comprises an axial edge of the catheter wall along the opening, and the cartridge is rotatable whereby the controlled movement of the cutting edge is arcuate.
 6. The device of claim 1 including:a drive member connected to the cartridge and contained within a lumen of the catheter, and movable near the proximal end of the catheter to impart like movement to the cartridge.
 7. The device of claim 1 wherein:said tissue cutting element is electrically conductive, and the energy source comprises a means for generating an electrical current in the cutting element to heat the cutting element and said adjacent tissue at least to said selected temperature.
 8. The device of claim 7 wherein:the means for generating an electrical current in the cutting element include a power supply, and first and second electrical conductors coupled to the power supply and further coupled to opposite ends of the cutting element.
 9. A process for removing body tissue, including:inserting a catheter into a body, and guiding the catheter to position a window of the catheter proximate selected tissue within the body; with the window so positioned, applying a force against the catheter in a direction to urge the window and wall portion of the catheter adjacent the window toward and against the selected tissue, to cause the selected tissue to enter the catheter through the window; and while the selected tissue is within the catheter, simultaneously using a cutting edge to cut tissue in a direction along the window and generating heat near the cutting edge to heat the selected tissue near the cutting edge during cutting, to sever the selected tissue for retention within the catheter.
 10. The process of claim 9 further including:after severing the selected tissue, closing the window to prevent egress of the selected tissue.
 11. The process of claim 9 wherein:said generating heat near the cutting edge to heat the selected tissue during said cutting tends to cauterize the tissue in the region of the cut.
 12. The process of claim 9 wherein:the cutting movement is substantially linear and axial with respect to the catheter.
 13. The process of claim 9 wherein:the cutting movement is arcuate, about an axis running longitudinally of the catheter.
 14. A process for removing selected tissue from a body, including:inserting an elongate catheter into a body, and guiding the catheter to selectively locate a tissue cutting element, carried by the catheter, adjacent selected tissue; and with said cutting element so selectively located, and while heating the cutting element to maintain the cutting element at least at a selected temperature above normal body temperature, manipulating the catheter to cause the cutting element to traverse a cutting path through the selected tissue whereby the heated cutting element simultaneously heats and cuts the selected tissue along the cutting path, to severe the selected tissue.
 15. The process of claim 14 further including:during said manipulating of the catheter, applying a force against the catheter in a direction to urge the cutting element toward and against tissue along the cutting path.
 16. The process of claim 15 wherein:the catheter includes a window near the cutting element for admitting tissue into the catheter, and said severing of the selected tissue is performed with the selected tissue extending into the catheter through the window.
 17. The process of claim 14 wherein:said causing of the cutting element to traverse the cutting path tends to cauterize tissue adjacent the cutting path.
 18. The process of claim 14 wherein:said cutting path is substantially linear and axial with respect to the catheter.
 19. The process of claim 14 wherein:said cutting path is arcuate, about an axis running longitudinally of the catheter.
 20. A device for removing selected tissue from a body, including:an elongate catheter having a proximal end and a distal end; a cutting element supported by the catheter in the region of the distal end; a position controller operatively coupled to the cutting element for providing a controlled movement of the cutting element; an energy source operatively coupled to the cutting element and adapted to heat the cutting element at least to a selected temperature of above normal body temperature, and for maintaining the cutting element at least at said selected temperature during said controlled movement; and wherein the catheter is flexible and maneuverable to locate the distal end of the catheter to position the cutting element adjacent a tissue wall segment whereby the cutting element, when undergoing the controlled movement, severs the adjacent tissue and heats the adjacent tissue while severing.
 21. The device of claim 20 further including:a structure adapted to urge the cutting element laterally against the selected tissue.
 22. The device of claim 21 wherein:the structure adapted to urge the cutting element includes a dilatation balloon mounted along the distal region, axially aligned with and on the opposite side of the catheter from the cutting element, and means for inflating the balloon.
 23. The device of claim 21 wherein:the structure adapted to urge the cutting element includes a flexible band axially aligned with and on the opposite side of the catheter from the cutting element.
 24. The device of claim 20 wherein:said cutting element is electrically conductive, and the energy source includes a electrical powder source for generating an electrical current in the cutting element.
 25. The device of claim 24 further includingfirst and second electrical conductors coupled to the power supply and respectively to opposite ends of the cutting element.
 26. The device of claim 24 further includingan indifferent electrode, a first conductor connected to the power source and to the cutting element, and a second conductor connected to the power source and to the indifferent electrode, to maintain the adjacent tissue at least at the select temperature primarily by ohmic heating, wherein the power source is an RF power source. 